The present disclosure relates to screw caps for containers.
Composite plastic and metal screw caps have been used for some types of containers, as exemplified by U.S. Pat. No. 5,346,082. The closure of the '082 patent includes an internally threaded plastic closure that goes over a metal disc. The disk is not attached to the plastic closure but is loosely retained therein. When the plastic closure is screwed onto the container, the metal disk is compressed against the rim of the container. A bead of plastisol sealant on the underside of the disk is compressed between the disk and the container rim to seal the container closed. This type of closure is sometimes used for retort containers.
It has been found that during retort processing, the seal can be breached because the plastisol sealant's ability to seal the container depends on a continuous compressive force from the plastic cap, which can be difficult to maintain.